The present invention relates to a mechanical pencil wherein a cartridge containing therein a number of leads is detachably mounted between a chuck which holds a lead at one end portion of the pencil and a push button provided at the other end. An operation of the push button causes the chuck to be opened or closed by the cartridge so that the lead may be advanced.
In conventional mechanical pencils of the type described above, lead cartridges of similar shape each of which contains therein leads of a predetermined diameter such as 0.1 mm, 0.2 mm, 0.5 mm, etc. are employed. Since each type of lead is enclosed within a similar shaped cartridge, there is possibility that a cartridge containing one type of leads is mounted in a mechanical pencil for leads of a different type. Such mismatching is often experienced by those who have two pencils or more using different types of leads, such as draftsmen. If, for example, a lead cartridge which contains leads 0.5 mm in diameter is mounted in a mechanical pencil which is designed for leads of 0.2 mm in diameter, the mechanical pencil does not work at all. Similarly, if a lead cartridge containing leads 0.1 mm in diameter is mounted in a pencil for leads 0.2 mm in diameter, the pencil does not work, either.